Usually, a microchip technique has been known that grooves of a size having the depth of 100 μm and the width of about 500 μm or smaller are formed on the surface of a substrate such as glass by a microfabrication technique such as a lithography, the grooves are employed as microchannels for liquid or gas to enable a chemical reaction, a biochemical reaction, a solvent extraction, a gas-liquid separation and further a chemical analysis or a non-contact optical analysis of a slight amount of components based on them.
As for the microchip technique, the inventors of this application also propose a measure that microbeads as reaction carriers are inserted into microchannels and dam shaped check parts are provided in the microchannels (document 1).
With the recent progress of molecular genetics or molecular biology and the expansion of the application thereof to a medical care, it has been a very important problem to extract nucleic acid from a liquid sample. Accordingly, the use of the microchip technique has been studied to extract the nucleic acid. A method using silica beads, a method using silica micropillars or a method using a silica film has been hitherto proposed (documents 2 to 4).
However, in the usual microchip technique, the method for extracting the nucleic acid by using, for instance, the silica micropillars or the silica filter undesirably has a basic problem that a cost is high and when the silica micropillars or the silica filter are stained, they cannot be replaced by new micropillars or a new silica film. Further, in the existing method using the microbeads such as silica, high pressure has been necessary to inject the microbeads into the microchannels. Thus, the microchannels have not been easily filled with the beads.
In the usual method for checking the microbeads by the dam shaped check parts, stagnation is liable to arise in the flow of the liquid sample so that the microbeads such as silica are inconveniently hardly smoothly transported.
Further, usually, when the microchannels are formed by using glass or quartz as the substrate of the microchip, dust is apt to be generated in the channels and the dust may be undesirably hardly removed.
Related documents are shown below. These documents are applied to this application with reference thereto.    1: K. Sato et al., Anal. Chem. 72, 1144-1147 (2000)    2: L. Ceriotti et al., (2002) Proceedings of the micro TAS 2002 symposium Nara, pp. 175-177    3: J. Kim et. al., (2002) Proceedings of the micro TAS 2002 symposium, Nara, pp. 224-226    4: Q. Wu et al., (2002) Proceedings of the micro TAS 2002 symposium, Nara, pp. 198-200